Cool optical illusion revisited

[Telecaster]

The Cornsweet edge, a variant of the checkerboard illusion, is making the social media rounds so I thought I'd link to a brief article explaining it.

http://www.americanscientist.org/issues/feature/2002/3/why-we-see-what-we-do/3

The illusion works due to the luminance gradients of the two squares at the edge where they meet. We learn through experience that such objects are highly likely to be of different luminosities, and so we come to see them as such even when they aren't. Visual confirmation bias.

Lest you continue to believe that you see things "as they are"… 

-Dave-

[Rob C]

Dave,

Always knew I wasn't cut out for being scientific. Thank you for proving me right!

;-)

Rob

[Isaac]

Used by landscape photographers.

[Telecaster]

Used by landscape photographers.

Bingo!

-Dave-

[Tim Lookingbill]

At least I know why those that do HDR seem to be not bothered when they edit a side lit brick house in a landscape to look too bright as if it has a giant white fill card lighting the opposing shadow side.

Why is it in all those scientific white papers that use science to explain how humans see and how cameras render color not one can produce a decent looking image as an example of how that knowledge is helpful or useful.

[amolitor]

This particular illusion is all over the place. It's a rare Ansel Adams print that doesn't deploy it somewhere. But it's not obvious. Obviously.

It's the basic method of creating the sensation of more tonal range, and you do it with dodging and burning.

Ming Thein recently posted a hilariously wrong essay on HDR recently in which he illustrates that he doesn't know this.

[Tim Lookingbill]

So that's your opinion of the photos in Glenn Randall's book?

Is Glen Randall's book a white paper that attempts to directly connect science to explain why and how humans create photos? I'm talking about the linked article that explains optical tricks involved in human perception but for some reason never ties it to why or how we can make fantastic looking images.

I didn't think Glenn Randall's book explains this, so I have no opinion of it.

[Tim Lookingbill]

This particular illusion is all over the place. It's a rare Ansel Adams print that doesn't deploy it somewhere. But it's not obvious. Obviously.

It's the basic method of creating the sensation of more tonal range, and you do it with dodging and burning.

And completely leaves out the adaptive effect of human perception which is constantly changing especially when dodging and burning in a red or amber colored darkroom. I worked in one for a commercial printer and I had to rely strictly AND completely on a stauffer step wedge to tell me when to pull the film out of the developer and into the stop bath. I was not making ANY aesthetic judgements until I viewed the final image on a light table. But I was turning continuous tone B&W photos into line conversions (halftone dots) so there was no relying on methods to overcome optical tricks and adaptive affects of the human visual system.

These optical illusions are all parlor tricks (infotainment) and a waste of time for photographers to keep in mind when trying to create images with impact.

[Isaac]

It's a rare Ansel Adams print that doesn't deploy it somewhere.

Please point to a specific example.

Ming Thein recently posted a hilariously wrong essay on HDR recently in which he illustrates that he doesn't know this.

Please provide a URI to the post.

[Telecaster]

Why is it in all those scientific white papers that use science to explain how humans see and how cameras render color not one can produce a decent looking image as an example of how that knowledge is helpful or useful.

I'm personally interested in the mechanisms of human vision primarily for the sake of pure understanding. Should physicists & biologists be required to offer photo workshops and image processing tips too? 

-Dave-

[AreBee]

Isaac,

Please provide a URI to the post.

I suspect this is it.

[Tim Lookingbill]

I'm personally interested in the mechanisms of human vision primarily for the sake of pure understanding. Should physicists & biologists be required to offer photo workshops and image processing tips too? 

-Dave-

Oh, I forgot this is the Coffee Corner and so this subject should be understood as FYI and have nothing to do with how to improve photography.

My mistake. I took the subject matter too seriously.

It's just in past discussions on this subject outside of off topic casual conversation online the very same science was used to convince/debate photographers that they can't trust their eyes to judge color and to use and trust a scientific instrument such as a spectrometer.

[amolitor]

If you need numerically accurate data about visual things, you definitely need instruments. Most of what you "see" is made up by your visual cortex, in some sense, which does an excellent job in certain dimensions and a terrible job in others.

If you need perceptually accurate data, though, your eyes are still pretty helpful. Some measurements would still not be amiss, for various reasons in various contexts.

[jjj]

Isaac, I suspect this is it.

If that is indeed the article Amolitor, why is it so bad? 

[Telecaster]

It's just in past discussions on this subject outside of off topic casual conversation online the very same science was used to convince/debate photographers that they can't trust their eyes to judge color and to use and trust a scientific instrument such as a spectrometer.

Yes, the notion that photographers must conform to any purportedly "objective" standard of color presentation is absurd. Most of us prefer that our photos look "normal"—whether per our individual judgment of such or a collective one—but this is convention rather than necessity.

A couple weeks ago, while attempting to pull shadow detail out of a photo, I pushed some values beyond my own "normal" and came up with the attached image. Not what I'd intended but I kinda like it.

-Dave-

[Rob C]

Dave -

Maybe this post is safe, but who knows - controversy is never far away. Enjoy:

https://www.youtube.com/watch?v=89_tkJekpbE

Rob C

[Telecaster]

Maybe this post is safe, but who knows - controversy is never far away. Enjoy:

https://www.youtube.com/watch?v=89_tkJekpbE

Good stuff.    I'd say the photography/music nexus is well-established. Particularly so IMO when guitars are involved! Mr. Clark is underrated, and you can't top Hank Sr. & Joe Pass.

I've attached a genre-appropriate guitar pic. It's a compositional misfire but since I haven't yet deleted it…

-Dave-

[NancyP]

Thanks for posting, I like these illusions.
It just goes to show, we aren't digital sensors.
One of the simple examples of how we differ - color invariance. Something you know to be a white object always "looks white" no matter what color temperature full-spectrum light you use on it. You, the human, do "Auto White Balance".